The ABEEM/MM Simulations Of Strontium (Ⅱ) And Barium (Ⅱ) Cation/water Systems

In this dissertation, the geometry optimization and vibration frequency calculation of strontium(â…¡) and barium(â…¡) cation water clusters M²⁺(H2O)n (n=1-6) in the gas phase at the MP2/6-31++G(d,p) level have been performed, and the energies have been calculated at the MP2/6-311++G(2d,2p) level with BSSE correction in the stablest conformation. The pseudopotential basis set LANL2DZ was employed for the metal cation. In terms of atom-bond electronegativity equalization fluctuating charge molecular force field (ABEEM/MM), we determined the parameters of the Sr(â…¡),Ba(â…¡)-water interaction potential. Then, the parameters were utilized into the study of the Sr(â…¡)/Ba(â…¡)-water clusters Sr²⁺/Ba²⁺(H2O)n (n=1-6), including structures,binding energies,vibration frequencies and so on, and the results are consistentted with those of the experiments or ab initio calculations. Furthermore, we employed these parameters to the dynamics simulations of Sr²⁺ and Ba²⁺ aqueous solution. The first peak of Sr²⁺/Ba²⁺-O radial distribution functions are located at 2.75?and 2.55?, respectively, and the coordination number of water molecules of the first hydration shell are 9.2 and 10.5, respectively, which show good consistency with those of the experiment and other simulations. We also calculated the distribution between the metal ion-oxygen vector and the dipole vector of water. The angle becomes wider and wider as the radius of the metal ion increases, which shows that the interaction between the metal ion and water gets weaker and weaker as the radius of the metal ion increases. Compared to the outer layer water molecules, the polarization effect of metal ion makes the bond length of the first hydration shell of water molecules longer, the bond angle∠HOH angle smaller, which is due to the attraction of metal ions to the oxygen atom and the repulsion of metal ions to the hydrogen atoms. The OH bond stretching vibration peaks in Sr²⁺/Ba²⁺ aqueous solution is located at 3500cm^-1, which moves to lower wave number about 200cm-1 compared with that of pure water.